Workpiece transfer apparatus

ABSTRACT

An apparatus for transferring workpieces to and from the chuck of a machine tool. A gripper arm is mounted to the machine frame for selectively axial and rotational movement on a shaft having helical and longitudinal threads on the surface thereof. A first nut is rotatably mounted to the machine frame for axial advancement of the shaft and a second nut is rotatably mounted for rotational advancement. The apparatus may also include a panel mounted to the machine frame between a transfer station and the chuck. An opening in the panel adjacent the transfer station has surfaces which mate with corresponding surfaces of the gripper arm so as to preclude the passage of debris to the transfer station. The apparatus may also include an apparatus for sequentially transferring a series of workpieces. The apparatus has a two gripper jaws and a compressible pusher plate therebetween which is compressed as it is moved towards an opening in an input chute so that a workpiece may roll between the jaws of the gripper.

FIELD OF THE INVENTION

The present invention relates to a workpiece transfer apparatus and moreparticularly, to a workpiece transfer apparatus for machine tools.

BACKGROUND OF THE INVENTION

In conventional machine tools, such as lathes, workpiece is securelysupported in a chuck during the machining operation. The chuck ismounted on one end of a spindle and the spindle is rotated so that atool may be brought into contact with the rotating workpiece. The toolhas a cutting edge which cuts into the workpiece to remove material sothat the workpiece can be machined to the desired shape and size. Thematerial thus cut from the workpiece by the tool may take the form ofdiscrete chips. If desirable, a liquid coolant may be used to lubricatethe cutting edge of the tool and to prevent heat buildup.

To automate the machining operation, it is desirable to provide anautomatic chuck which can be controlled to selectively grip or release aworkpiece disposed within the jaws of the chuck. To more fully automatethe machining operation, however, it is also desirable to provide aworkpiece transfer apparatus for loading workpieces into the chuckbefore the machining operation is performed and for unloading theworkpieces from the chuck after the machining operation has beencompleted. The workpiece transfer apparatus may pick up unmachinedworkpieces from a loading station such as a chute or bin adjacent to themachine tool. In addition, the workpiece transfer apparatus may unloadworkpieces from the chuck and transfer them to an unloading station suchas a chute or bin adjacent to the machine tool.

Conventional workpiece transfer devices may include a moveable shafthaving a workpiece gripping mechanism mounted on one end thereof. Suchshafts are typically moveable axially along the shaft axis, known in theart as the "Z direction," and may also be moveable rotationally aboutthe shaft axis, known in the art as the "C direction". Such workpiecetransfer devices may include a motor for providing the rotationalmovement in the C direction and a hydraulic or pneumatic cylinder foradvancing and withdrawing the shaft along its axis in the Z direction.These transfer devices therefore require both an electrical power sourcefor the rotational motor and a separate hydraulic or pneumatic powersource for moving the shaft axially.

Another type of workpiece transfer device is disclosed in U.S. Pat. No.4,646,422 to McMurtry. The device of the McMurtry patent comprises atransfer mechanism including a shaft supported at both ends for rotationthereof. An arm is supported on the shaft for movement along the axis ofthe shaft but is fixed against rotation relative to the shaft. A firstmotor rotates the shaft and a second motor rotates a threaded rod insidethe shaft to move the arm in an axial direction along the shaft. Theshaft, however, extends substantially between the tool and chuck of themachine and thus limits access to the machining area. In addition, theworkpiece transfer mechanism is subjected to chips and coolant producedby the machining operation.

Another type of workpiece transfer device is disclosed in U.S. Pat. No.4,458,566 to Tajima. The Tajima patent discloses a device having an armsecured to the end of a moveable shaft. The shaft of the Tajima patentis moveable both axially and rotationally about its axis. However,rotational movement is provided by a threaded rod which is mountedperpendicularly to the arm axis and, as such, is limited to rotationthrough an arc determined in part by the length of the rod. Such limitedrotational movement limits the loading and unloading capability of thearm.

The chips and coolant produced by the machining operation are oftenexpelled from the vicinity of the tool in unpredictable trajectories.Moreover, errant chips and coolant can be detrimental to the machinetool. For example, chips may interfere with the operation of the gripperdevices used for loading and unloading workpieces. Thus, it is desirableto confine chips and coolant to the immediate vicinity of the machiningoperation.

The workpiece gripping mechanisms of conventional workpiece transferdevices typically include a three-jawed chuck and a pusher platespring-loaded between the jaws. The workpieces are picked up from anopening at the end of a declining input chute by the gripping mechanismand are transferred to the chuck. A workpiece is positioned at theopening of the chute and is restrained from falling through the openingby a moveable shutter. The gripping mechanism is moved towards theworkpiece, the shutter is opened and the pusher plate engages theworkpiece. The jaws are then closed and the workpiece can be removedfrom the chute.

More workpieces may be restrained further up the input chute so as notto interfere with the operation of the three jaws of the grippingmechanism. The workpieces may be restrained by two retractable gatesoperating in an escapement fashion so as to allow only one workpiece ata time to advance to the opening. Workpiece transfer devices of thistype thus require the provision of a moveable shutter and tworetractable gates which adds to the expense and complexity of thetransfer apparatus.

It is therefore an object of the present invention to provide animproved workpiece transfer apparatus for machine tools.

It is still another object of the present invention to provide animproved workpiece transfer apparatus which allows full access to themachining area and which has improved mobility.

It is yet another object of the present invention to provide an improvedmachine tool which provides improved confinement of chips and coolantproduced during the machining operation.

It is yet another object of the present invention to provide an improvedwork transfer apparatus having fewer actuated components.

SUMMARY OF THE INVENTION

These and other objects and advantages of the present invention areachieved in the embodiments illustrated herein by the provision of anapparatus for transferring workpieces having a gripper arm supported ona shaft and moveable both rotationally and axially by a pair ofrotatable nuts on the shaft.

The apparatus includes a machine frame and means for mounting thegripper arm thereto so as to permit selective rotational movement aboutan axis and selective axial movement along the axis. The mounting meansincludes the drive shaft mounted for rotation about the axis and havingthe gripper arm mounted on one end of the shaft. The drive shaft has atleast one helical thread and one longitudinal thread on the surfacethereof, which threads may comprise one or more grooves formingdepressions in the surface of the shaft.

A first nut is rotatably mounted on the drive shaft and is fixed to themachine frame against axial movement. The first nut has an internalthread which engages the helical thread of the shaft. The internalthread may comprise a series of balls retained in the nut and entrainedwithin the helical groove. The first nut is selectively rotated by afirst reversible drive motor so as to axially advance or retract theshaft.

A second nut is also rotatably mounted on the drive shaft and is fixedto the machine frame against axial movement. The second nut has aninternal thread which engages the longitudinal thread of the shaft. Theinternal thread may comprise a series of balls retained in the nut andentrained within the longitudinal groove. The second nut is selectivelyrotated by a second reversible drive motor so as to cause rotationalmovement of the shaft about the axis.

The apparatus may also include control means for selectively operatingthe first and second motors so that the gripper arm can be moved betweena first position adjacent the transfer station and a second positionadjacent the work station such as may be desirable when the first andsecond positions are both axially and rotationally offset from eachother. The control means may also include brake means which acts on thesecond drive motor so as to prevent unwanted rotation of the shaft. Inthis manner, the shaft can be moved in a purely axial direction withoutany rotation.

A workpiece loading means and workpiece unloading means may be mountedto the machine frame at the transfer station so as to define respectiveloading and unloading stations. The gripper arm may also include firstand second gripper jaw assemblies for releasably engaging and supportinga workpiece. The first and second gripper jaw assemblies are positionedadjacent each other such that they may be simultaneously positioned atthe loading and unloading stations respectively by the control means.

The gripper jaw assemblies may each include jaw means. The jaw means ofthe first gripper assembly may include two jaws and the jaw means of thesecond gripper assembly may include three jaws, the respective jawsbeing selectively moveable towards and away from each other.

A machine tool is provided in another aspect of the invention havingprovision for transferring a workpiece between a transfer station and amachining station. The machine tool has a panel mounted to the machineframe so as to have the transfer station, defined by a workpiecetransfer means, on one side thereof and the machining station, definedby the machine tool chuck, on the other side thereof. The panel has anopening therethrough adjacent to the transfer station.

The machine tool has a gripper arm having at least one gripper jawassembly and means mounting said gripper arm to the machine frame sothat the gripper arm is on the same side of the panel as the chuck. Themounting means provides selective movement of the gripper arm between afirst position wherein the gripper jaw assembly extends through theopening and is adjacent the transfer station, and a second positionwherein the gripper jaw assembly is adjacent the chuck. The mountingmeans may include a drive shaft mounted for rotation about an axis,first drive means for axially advancing or retracting the drive shaftalong the axis, and second drive means for rotating the shaft about theaxis. The first and second drive means may be mounted on the same sideof the panel as the transfer station.

The gripper arm and the panel have mating surfaces which cooperate toform a seal surrounding the opening when the gripper arm is in the firstposition. This precludes debris such as chips and coolant from passingthrough the opening and reaching the gripper jaw assembly when thegripper arm is in the first position.

In another aspect of the invention, an apparatus for sequentiallytransferring a series of workpieces from a transfer station is providedand includes a gripper arm moveable towards and from the transferstation. The gripper arm includes a pair of releasable jaws for engaginga workpiece when at the transfer station and a compressible pusher platefor engaging a workpiece gripped in the jaws. Stop means is provided forcompressing the pusher plate as it is moved towards the transferstation. Chute means is provided for advancing one of the workpieces tothe transfer station when the gripper arm is positioned adjacent thetransfer station so that the workpiece will be positioned between thejaws. Chute means may include a bottom rail declined towards thetransfer station, a bumper at the end of the bottom rail and first andsecond side rails extending generally to the transfer station with thefirst side rail having an opening therein adjacent the transfer station.

BRIEF DESCRIPTION OF THE DRAWINGS

Some of the objects and advantages of the present invention have beenstated, others will appear as the description proceeds when taken inconjunction with the accompanying drawings in which;

FIG. 1 is a perspective view of a machine tool having the work transferapparatus according to the present invention mounted thereon;

FIG. 2 is a schematic view of the workpiece transfer apparatus of thepresent invention;

FIG. 3 is a front elevational view of the workpiece transfer apparatusof the present invention taken along lines 3--3 of FIG. 1 wherein partof the gripper arm head is cut away to show the first gripper jawassembly;

FIGS. 4A through 4C are front elevational views of the workpiecetransfer apparatus of the present invention, illustrating sequentiallythe steps taken in loading and unloading workpieces to and from thechuck;

FIG. 5 is a front elevational view of the panel of the present inventionshown without the workpiece transfer apparatus;

FIG. 6 is a perspective and exploded view of the gripper armillustrating the drive shaft and the gripper jaw assemblies;

FIG. 7 is an enlarged sectional view of the drive shaft of the workpiecetransfer apparatus of the present invention, taken along lines 7--7 ofFIG. 6;

FIG. 8 is a sectional view of the workpiece transfer apparatus of thepresent invention taken along lines 8--8 of FIG. 3; and

FIG. 9 is a sectional view of the workpiece transfer apparatus of thepresent invention taken along lines 9--9 of FIG. 3.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

Referring more particularly to the drawings, FIG. 1 illustrates amachine tool 10 for machining workpieces 11 having a workpiece transferapparatus 12 according to the present invention mounted thereto. Themachine tool 10 includes a machine frame 13 and a motor driven spindle14 rotatably supported thereon. Mounted on one end of the spindle 14 isa chuck 15 which preferably comprises an automatic chuck of the typewherein workpieces 11 may be selectively gripped and released.

The chuck 15 extends into a machining enclosure 16 which is defined byseveral walls 17 and a door 20, as discussed in more detail below. Atool turret 21 capable of supporting one or more tools 22 is alsodisposed within the machining enclosure 16. The tool turret 21 ismounted such that a selected tool 22 may be brought into contact withthe workpiece 11 and the desired machining operation performed thereon.

Also disposed within the machining enclosure 16 is a gripper arm 23 fortransferring workpieces 11 to and from the chuck 15. Mounting means 29support the gripper arm 23 on the machine frame 13 for axial androtational movement. The gripper arm 23, as shown in FIG. 6, is securelyattached to one end of a moveable drive shaft 24 by dowel pins 25 andlocking screws 26. The radially outward end of the gripper arm 23includes a head 18 whereon first and second gripper jaw assemblies 27,28 may be mounted, as discussed in more detail below.

The drive shaft 24 defines an axis 30, and is mounted to the machineframe 13 for selective movement longitudinally along its axis, i.e., theZ direction, and rotationally about its axis, i.e., the C direction. Thedrive shaft 24 has at least one helical thread 31 and at least onelongitudinal thread 32 formed thereon which extend along the length ofthe shaft 24.

As shown in FIG. 2, the drive shaft 24 is partially supported by firstdrive means 38 including a first nut 33 having at least one internalhelical thread 34 engaging the helical thread 31 of the drive shaft 24.The first nut 33 is mounted to the machine frame 13 so as to allowrotation thereof but is fixed against axial movement along the axis 30of the drive shaft 24, as shown in FIG. 8. The first nut 33 is connectedto a first reversible drive motor 35 via a belt 36 so as to allowselective rotation of the first nut 33. Accordingly, as the nut 33 isrotated in one direction, the nut thread 34 advances along the shaftthread 31 and the shaft 24 is axially moved in a Z direction (dependingon the helical orientation of the thread) relative to the axially fixednut. Conversely, if the nut 33 is rotated in the other direction, theshaft 24 is moved axially in the opposite direction.

The helical shaft thread 31 may comprise a groove formed on the outersurface of the shaft 24 as shown in FIGS. 6 and 7. Alternatively, thehelical thread 31 may comprise a raised thread extending on the surfaceof the drive shaft 24, such as a screw thread. In addition, more thanone thread could be used so that, in the case of two threads, the shaft24 would have a double helix thread pattern.

The internal thread 34 of the nut 33 preferably comprises a series ofballs 37 arranged in a helical fashion within the nut 33, conventionallyreferred to as a ball screw. The balls 37 are restrained within the nut33 but are free to rotate therein. Alternatively, the nut 33 maycomprise a nut of the recirculating type wherein the balls 37recirculate through the nut. Accordingly, the entrained balls 37 rollalong the helical groove of the drive shaft 24 as the nut 33 is rotated.

As shown in FIG. 2, the drive shaft 24 is also supported by second drivemeans 39 comprising a second nut 40 having at least one internallongitudinal thread 41 engaging the longitudinal thread 32 of the driveshaft 24. The second nut 40 is also mounted to the machine frame 13 soas to allow rotation thereof and is fixed against axial movement alongthe axis 30 of the drive shaft 24, as shown in FIG. 9. The second nut 40is connected to a second reversible drive motor 42 via a belt 43 so asto allow selective rotation of the second nut 40. Accordingly, as thesecond nut 40 is rotated, the internal thread 41 of the nut 40 engagesthe longitudinal thread 32 of the drive shaft 24 and causes rotationalmovement of the drive shaft about its axis 30 in the C direction. Thesecond reversible drive motor 42 may also include a selectively operablebrake 44 for preventing rotation of the second nut 40 and therefore thedrive shaft 24.

The longitudinal shaft thread 32 may comprise one or more grooves formedon the outer surface of the shaft 24 and extending parallel to the axis30 of the shaft 24. Preferably, as shown in FIGS. 6 and 7, thelongitudinal shaft thread 32 comprises three pairs of grooves spacedevenly about the periphery of the shaft 24. Alternatively, thelongitudinal thread 32 may comprise one or more raised threads extendingalong the drive shaft 24, such as one or more splines.

The internal thread 41 of the nut 40 preferably comprises one or moreseries of balls 45 arranged longitudinally within the nut 40. The balls45 are restrained within the nut 40 but are free to rotate therein.Alternatively, the second nut 40, may also be of the recirculating type.Accordingly, the entrained balls 45 roll along the longitudinal groovesof the drive shaft 24 as the shaft is moved axially through the nut 40.

Accordingly, to move the gripper arm 23 in the Z direction the firstdrive motor 35 is operated. The shaft 24 may, however, have a tendencyto rotate which may be caused by torque applied to the shaft 24 by theoperation of the first nut 33 or by the radially extended weight of thegripper arm 23 and any workpiece 11 gripped therein. Thus, to preventany unwanted rotation, the brake 44 associated with the second motor 42may be engaged.

To rotate the gripper arm 23, the brake 44 is disengaged and the secondmotor 42 is operated. Thus, while the shaft 24 is being rotated, thefirst nut 33 rotates with the shaft and does not move rotationallyrelative to the shaft.

A control means 46, such as a computer or other controller, is alsoprovided to control the operation of both motors 35, 42 and the brake44. The controller may be programmed by an operator through a controlpanel 47 mounted on the machine tool 10, as shown in FIG. 1. The controlmeans 46 may also control the other functions the machine tool 10 suchas, for example, the opening and closing of the automatic chuck 15, therotation of the spindle 14 and the movement of the tool 22 relative tothe workpiece 11, such that a fully automated machining operation may becoordinated. Thus, the gripper arm 23 may be moved in the Z direction orthe C direction, or any combination thereof, by selective sequential orsimultaneous operation of the respective drive motors 35, 42.

The workpiece transfer apparatus 12 according to the present inventionthus can transfer workpieces 11 between two positions which may be bothaxially and laterally offset from each other. For example, the workpiece11 may be transferred between a first position for loading a workpiece11, as shown in FIG. 8, and a second position adjacent a work station49, as shown in FIG. 9. A work station 49 according to the presentinvention may comprise a machining station 50 such as the automaticchuck 15 discussed above. The first position for loading a workpiece 11is discussed in more detail below.

A workpiece transfer means 51 may be mounted to the machine frame 13, asshown in FIG. 3. The workpiece transfer means 51 may comprise a loadingmeans 52 and an unloading means 53. The workpiece loading means 52 hasan input chute means 54 which extends downwardly to the machine frame13. Unmachined workpieces 11 are placed on the chute 54 by an operatoror by an automated conveyor (not shown), and roll downwardly towards abumper 55 at the end of the chute 54. The end of the chute 54 thusdefines a loading station 56 from which unmachined workpieces 11 areloaded into the first gripper jaw assembly 27 mounted on the head 18 ofthe gripper arm 23.

The workpiece unloading means 53 may comprise an output chute 57extending downwardly away from the machine frame 13. The upper end ofthe output chute 57 defines an unloading station 60 at which machinedparts 11a are unloaded from the second gripper jaw assembly 28.

The unloading station 60 is adjacent to the loading station 56 and thefirst and second gripper jaw assemblies 27, 28 are laterally offset fromeach other by a distance equal to the distance between the loading andunloading stations 56, 60. Accordingly, the first and second gripper jawassemblies 27, 28 may be simultaneously positioned at the loading andunloading stations 56, 60, respectively.

The operation of the workpiece transfer apparatus 12 of the presentinvention is shown in FIGS. 4A through 4C. As shown in this sequence, aworkpiece 11a which has just been machined is replaced in the chuck 15with an unmachined workpiece 11. Starting with FIG. 4A, when the gripperarm 23 is in the first position, an unmachined workpiece 11 is loadedinto the first gripper jaw assembly 27 at the workpiece loading station56, as shown in FIG. 8. The gripper arm 23 is then moved axially awayfrom the first position by operation of the first motor 35, as discussedabove and as shown in phantom in FIG. 8. The brake 44 of the secondmotor 43 may be simultaneously engaged to prevent unwanted rotation ofthe gripper arm 23. The brake 44 is then released and the second motor42 is operated so that the gripper arm 23 is rotated downwardly to theposition shown in FIG. 4B.

The brake 44 is engaged and the first motor 35 is operated in theopposite direction so that the gripper arm 23 is moved axially inwardlytowards the chuck 15. The second gripper jaw assembly 28 then picks up amachined workpiece lla from the automatic chuck 15. The first motor 35is again engaged and the gripper arm 23 is moved axially away from thechuck 15. The gripper arm 23 is rotated further downwardly to theposition shown in FIG. 4C and the gripper arm 23 is moved axiallyinwardly, also as shown in FIG. 9. The first gripper jaw assembly 27 isreleased and the unmachined part is deposited in the automatic chuck 15.The gripper arm 23 is then rotated upwardly to the position shown inFIG. 4A, and the gripper arm is moved axially inwardly to again assumethe first position. The second gripper jaw assembly 28 is subsequentlyreleased and the machined workpiece 11a rolls away from the unloadingstation 60 on the output chute 57. The output chute 57 may empty into abin or onto a conveyor.

As shown in FIG. 1, the chuck 15, gripper arm 23 and tool turret 21 aredisposed within the machining enclosure 16. The enclosure 16 is definedby several walls 17 and a moveable door 20 and confines chips andcoolant within the enclosure to protect other machine tool 10 parts andthe machine tool operator.

One of the walls 17 of the enclosure 16 comprises a panel 61 mounted tothe machine frame 13 so as to have a transfer station 62, such as theloading station 56 and/or unloading station 60 discussed above, on oneside thereof. The panel 61 is also mounted so as to have the chuck 15 onthe other side of the panel from the transfer station 62. The panel 61has a first opening 63 therethrough which is adjacent to the transferstation 62. The panel 61 may also have a second opening 64 through whichthe shaft 24 of the gripper arm 23 extends. The respective openings ofthe panel 61 and their relationship to the chuck 15 are best shown inFIG. 5. When the gripper arm 23 is in the first position, the gripperjaw assemblies 27, 28 extend through the first opening and are adjacentthe respective transfer station 62. When the gripper arm 23 is in thesecond position, the gripper jaw assemblies 27, 28 are adjacent thechuck 15.

To move the gripper arm 23 of the present invention to the firstposition, the gripper arm 23 is rotated until the head 18 is in axialalignment with the first opening 63. The gripper arm 23 is then movedaxially toward the opening 63 so that the first and second gripper jawassemblies, 27, 28 according to the embodiment discussed above, movethrough the opening to the loading 56 and unloading stations 60respectively.

As is clearly seen in FIG. 3, the size and shape of the first opening 63corresponds to the size and shape of the head 18 of the gripper arm 23.In addition, the head 18 has a flange 65 surrounding the gripper jawassemblies 27, 28 so as to provide a surface to mate against the panelsurface 67 surrounding the opening. Thus, when the gripper arm 23 ismoved to the first position, the gripper jaw assemblies 27, 28 arebehind the panel 61 relative to the cutting area and are shielded fromchips and coolant by the head 18 of the gripper arm 23. Preferably, anelastomeric seal 66 may be affixed to the flange 65 of the gripper armhead 18 so as to provide an improved seal with the panel surface 67.

The panel 61 may also include a second opening 64 positioned such thatthe drive shaft 24 extends axially therethrough. The gripper arm 23 mayalso mate with the panel surface 68 surrounding the second opening 64 topreclude the passage of debris to the first and second drive means 38,39. An elastomeric seal 66a may also be provided to seal the secondopening 64.

The gripper arm 23 may also include an extensible cover 69 surroundingthe shaft 24. In a preferred embodiment, the cover 69 comprises atelescoping tube which extends from the gripper arm 23 to at least thepanel 61, and may extend through the second opening 64 to the second nut40, as shown in FIG. 9. The cover 69 ensures that chips and coolant donot interfere with action of the shaft 24 and rotatable nuts 33, 40.

The gripper jaw assemblies 27, 28 may each include jaw means 70, 71, asshown in FIG. 6, for selectively gripping and releasing workpieces 11.The jaw means 70 of the first gripper jaw assembly 27 may include twomoveable jaws 72 which are selectively moveable towards and away fromeach other. The jaw means 71 of the second gripper jaw assembly 28 mayinclude three moveable jaws 73 which are selectively moveable towardsand away from each other. The moveable jaws 72, 73 are pneumaticallyactuated by air hoses 74 extending through the gripper arm 23 and thedrive shaft 24 to a compressed air source (not shown).

The gripper jaw assemblies 27, 28 may each also include a compressiblepusher plate 75 interposed between the moveable jaws 72, 73. The pusherplates 75 are generally circular and of a larger diameter than theworkpieces 11 and may be mounted to the gripper arm 23 on spring-loadedslides 76. Accordingly, in the case of the second gripper jaw assembly28, the pusher plate 75 contacts the workpiece 11a and is compressed asthe gripper jaw assembly 28 is moved towards the chuck 15. Thus, whenthe gripper jaws 72, 73 are in the closed position and the workpiece 11is gripped therein, the pusher plate 75 maintains a force against theworkpiece.

When the workpiece 11 is then moved to either the chuck 15 (as with thefirst gripper jaw assembly 27) or to the unload station 60 at the outputchute 57 (as with the second gripper jaw assembly 28) the workpiece 11will be pushed away from the gripper arm 23 when the jaws 72, 73 areopened. This is desirable because the action of the pusher plate 75ensures that the workpiece 11 is firmly seated in the chuck 15 or outputchute 57 as the jaws 72, 73 are released and the gripper arm assembly 23is moved away from the workpiece 11.

As shown in FIG. 8, the input chute means 54 may include one or morebottom rails 77 and first and second side rails 81, 82 for supporting anunmachined workpiece 11 as it rolls down the input chute 54. A bumper 55is located at the bottom end of the chute 54 and a proximity sensor 79may be positioned adjacent thereto to sense workpieces 11 at the bottomof the chute 54. The bottom of the input chute 54 thus defines theloading station 56.

The input chute 54 is also provided with a retractable gate 80 locatedbetween the two lowermost workpiece positions which can restrainworkpieces 11 from rolling to the end of the chute 54. The operation ofthe gate 80, as discussed in more detail below, may be controlled by thecontrol means 46 in response to signals from the sensor 79.

The first side rail 81 facing the gripper arm 23 does not completelyextend to the bumper 55 so that an opening 83 is formed at the lowermostend of the input chute 54. The second side rail 82 extends completely tobumper 55. When picked up by the first gripper jaw assembly 27, theworkpiece 11 may be removed from the input chute 54 through the opening83 in the first side rail 81.

Stop means 84 comprising one or more pusher plate stops are locatedadjacent to the first side rail opening 83 and may be fixed to the inputchute 54. The stops 84 extend into the opening 83 by an amountsufficient to contact and compress the pusher plate 75 as it is movedtowards the unload station 60. The stops 84 are also generally coplanarwith the inner surface of the first side rail 81. Accordingly, when thefirst gripper jaw assembly 27 is moved to the loading station 56 and thejaws 72 extend into the input chute 54, the pusher plate 75 iscompressed against the fixed stops 84 and forms a temporary extension ofthe first side rail 81 over the opening 83, as explained in more detailbelow.

Workpieces 11 are loaded into the first gripper jaw assembly 27 asfollows. Immediately after an unmachined workpiece 11 has been removedfrom the input chute 54, the remaining workpieces in the input chute arerestrained by the retractable gate 80, which remains in the loweredposition. Accordingly, at this point there is not a workpiece at theloading station 56.

After the workpiece 11 has been placed in the chuck 15, the jaws 72 ofthe first gripper jaw assembly 27 are opened and the gripper arm 23returns to the first position as discussed above. The gripper arm 23 ismoved towards the panel 61 so that the open jaws 72 of the first gripperjaw assembly 27 extend into the input chute 54 through the opening 83.Also, the pusher plate 75 is compressed against the stops 84 when thegripper jaw assembly 27 is moved to this position. The machiningoperation can now be performed and, as discussed above, the position ofthe gripper arm head 18 prevents chips and coolant from passing throughthe opening and interfering with the operation of the gripper jawassemblies 27, 28.

At sometime during the machining operation, the retractable gate 80 isopened and the next unmachined part is allowed to roll down until itstrikes the bumper 55. Only one retractable gate is necessary, unlikethe two gate escapement of conventional devices discussed above, becausewhen the gate 80 is opened, only one workpiece 11 can advance. Thatworkpiece rests against the bumper 55 and the next workpiece restsagainst the first at a position behind the gate 80. This is not possiblewith conventional devices because the next in line workpiece wouldinterfere with the operation of the conventional three jawed gripperassembly. Thus, the gate 80 can be closed for the next cycle and onlyone workpiece 11 will have been advanced.

As the lowermost workpiece rolls toward the bumper 55 it is supported bythe bottom rail 77, the second side rail 82 and the pusher plate 75which, as discussed above, is generally coplanar with the first siderail 81 facing the gripper arm 23. This arrangement allows the workpiece11 to be fully supported from three sides and the compressed pusherplate 75 acts as an extension of the first side rail 81. Also, theopened two jaws 72 of the first gripper jaw assembly 27 allow theworkpiece 11 to roll into the position defined as the loading station 56so that, when the jaws 72 are closed, the workpiece 11 will be securelygripped. After the contemporaneous machining operation has beencompleted, the unmachined workpiece 11 can then be withdrawn from theinput chute 54 through the opening 83. The pusher plate stops 84 do notextend into the opening 83 to an extent which would interfere with theremoval of the workpiece 11.

In the drawings and specification, preferred embodiments of theinvention have been illustrated and described, and althoughspecifications are employed, they are used in a generic and descriptivesense and not for the purposes of limitation.

That which is claimed is:
 1. An apparatus for transferring a workpiecebetween two positions which are offset from each other, and comprisingamachine frame, a gripper arm including at least one gripper jaw assemblyfor releasably engaging and supporting a workpiece, means mounting saidgripper arm to said machine frame for selective movement about an axiswhich is fixed with respect to said machine frame, and for selectiveaxial movement in the direction of said axis, said mounting meanscomprising(a) a drive shaft mounted for rotation about said axis andhaving at least one helical thread and at least one longitudinal threadon the surface thereof, (b) a first nut mounted on said drive shaft andfixed against axial movement along the axis and having an internalthread engaging said one helical thread of said shaft, (c) a firstreversible drive motor for selectively rotating said first nut so as tocause said shaft to axially advance or retract, (d) a second nut mountedon said shaft and fixed against axial movement along the axis and havingan internal thread engaging said one longitudinal thread of said driveshaft, (e) a second reversible drive motor for selectively rotating saidsecond nut and so as to cause rotational movement of said shaft aboutthe axis.
 2. The apparatus as defined in claim 1 further comprisingcontrol means for selectively operating said first and second motors soas to move said gripper arm between a first position for loading aworkpiece and a second position adjacent a work station and wherein thefirst and second positions are axially offset from each other in thedirection of the axis and rotationally offset from each other about theaxis.
 3. The apparatus as defined in claim 2 further comprisingaworkpiece loading means mounted to said machine frame and which definesa loading station, a workpiece unloading means mounted to said machineframe and which defines an unloading station which is adjacent saidloading station, and wherein said gripper arm comprises first and secondgripper jaw assemblies each of which includes jaw means for releasablyengaging a workpiece, and with the first and second gripper jawassemblies being positioned with respect to each other so that they maybe simultaneously positioned at said loading and unloading stationsrespectively by said control means.
 4. The apparatus as defined in claim3 wherein said jaw means of said first gripper jaw assembly comprisestwo jaws selectively movable towards and away from each other.
 5. Theapparatus as defined in claim 3 wherein said jaw means of said secondgripper jaw assembly comprises three jaws selectively movable towardsand away from each other.
 6. The apparatus as defined in claim 2 whereinsaid control means further comprises brake means for selectivelypreventing rotation of said shaft.
 7. The apparatus as defined in claim6 wherein said brake means is connected to said second reversible drivemotor to selectively prevent rotation of said motor and said shaft. 8.The apparatus as defined in claim 1 wherein said one helical thread ofsaid shaft comprises a helical groove formed in the surface of saidshaft.
 9. The apparatus as defined in claim 8 wherein said internalthread of said first nut comprises a series of balls entrained in saidhelical groove.
 10. The apparatus as defined in claim 1 wherein said onelongitudinal thread of said shaft comprises a longitudinal groove formedin the surface of said shaft.
 11. The apparatus as defined in claim 10wherein said internal thread of said second nut comprises a series ofballs entrained in said longitudinal groove.
 12. A machine tool forautomated transfer and machining of workpieces comprising:a machineframe, a chuck rotatably mounted to said machine frame for supporting aworkpiece during machining and defining a machining station, a workpiecetransfer means mounted to said machine frame and defining a transferstation, a gripper arm including at least one gripper jaw assembly forreleasably engaging and supporting a workpiece, and means mounting saidgripper arm to said machine frame for selective movement about an axiswhich is fixed with respect to said machine frame, and for selectiveaxial movement in the direction of said axis, so that said one gripperjaw assembly is moveable between said machining station and saidtransfer station, said mounting means comprising(a) a drive shaftmounted for rotation about said axis and having at least one helicalthread and at least one longitudinal thread on the surface thereof, (b)a first nut mounted on said drive shaft and fixed against axial movementalong the axis and having an internal thread engaging said one helicalthread of said shaft, (c) a first reversible drive motor for selectivelyrotating said first nut so as to cause said shaft to axially advance orretract, (d) a second nut mounted on said shaft and fixed against axialmovement along the axis and having an internal thread engaging said onelongitudinal thread of said drive shaft, (e) a second reversible drivemotor for selectively rotating said second nut and so as to causerotational movement of said shaft about the axis.
 13. The machine toolas defined in claim 12 further comprising control means for selectivelyoperating said first and second motors so as to move said gripper armbetween said machining station and said transfer station and wherein themachining and transfer stations are axially offset from each other inthe direction of the axis and rotationally offset from each other aboutthe axis.
 14. The machine tool as defined in claim 12 wherein saidworkpiece transfer means comprises a workpiece loading means defining aloading station, and a workpiece unloading means defining an unloadingstation, and wherein said gripper arm comprises first and second gripperjaw assemblies each of which includes jaw means for releasably engaginga workpiece, and with the first and second gripper jaw assemblies beingpositioned with respect to each other so that they may be simultaneouslypositioned at said loading and unloading stations respectively by saidcontrol means.
 15. The machine tool as defined in claim 14 wherein saidjaw means of said first gripper jaw assembly comprises two jawsselectively movable towards and away from each other.
 16. The machinetool as defined in claim 14 wherein said jaw means of said secondgripper jaw assembly comprises three jaws selectively movable towardsand away from each other.
 17. The machine tool as defined in claim 13wherein said control means further comprises brake means for selectivelypreventing rotation of said shaft.
 18. The machine tool as defined inclaim 17 wherein said brake means is connected to said second reversibledrive motor to selectively prevent rotation of said motor and saidshaft.
 19. The machine tool as defined in claim 12 wherein said onehelical thread of said shaft comprises a helical groove formed in thesurface of said shaft.
 20. The machine tool as defined in claim 19wherein said internal thread of said first nut comprises a series ofballs entrained in said helical groove.
 21. The machine tool as definedin claim 12 wherein said one longitudinal thread of said shaft comprisesa longitudinal groove formed in the surface of said shaft.
 22. Themachine tool as defined in claim 21 wherein said internal thread of saidsecond nut comprises a series of balls entrained in said longitudinalgroove.
 23. A machine tool having provision for transferring a workpieceto and from a machining station and comprisinga machine frame, aworkpiece transfer means mounted to said machine frame and defining atransfer station, a chuck mounted to said machine frame for engaging andsupporting a workpiece during a machining operation, at least one panelmounted to said machine frame so as to have said transfer station on oneside thereof and said chuck on the other side thereof, said one panelhaving only one opening therethrough adjacent said transfer station, agripper arm including first and second gripper jaw assemblies forreleasably engaging and supporting a workpiece, means mounting saidgripper arm to said machine frame so that said gripper arm is on thesame side of said panel as said chuck and for movement between a firstposition wherein said first and second gripper jaw assemblies extendthrough said one opening and are adjacent said transfer station, and asecond position wherein said first and second gripper jaw assemblies areadjacent said chuck, and said gripper arm and said panel having matingsurfaces which form a seal surrounding said one opening when saidgripper arm is in said first position and said first and second gripperlaw assemblies extend through said one opening so as to preclude debrisfrom passing through the opening during the machining operation.
 24. Themachine tool as defined in claim 23 wherein said means mounting saidgripper arm comprises a drive shaft mounted for rotation about an axis,first drive means for axially advancing or retracting said drive shaftalong said axis, and second drive means for rotating said shaft aboutsaid axis, and with said first and second drive means being positionedon the same side of said panel as said transfer station.
 25. The machinetool as defined in claim 24 wherein said panel includes a second openingpositioned so that said drive shaft extends axially therethrough, andwherein said gripper arm further comprises an extensible coversurrounding said shaft and extending between said panel and said gripperarm to preclude debris formed during the machining operation fromcontacting said shaft.
 26. The machine tool as defined in claim 23wherein said workpiece transfer means comprises a workpiece loadingmeans defining a loading station, and a workpiece unloading meansdefining an unloading station, and wherein said gripper arm comprisesfirst and second gripper jaw assemblies each of which includes jaw meansfor releasably engaging a workpiece, and with the first and secondgripper jaw assemblies being positioned with respect to each other sothat they are both positioned to extend through said first opening tooperatively engage said loading and unloading stations respectively insaid first position of said gripper arm.
 27. The machine tool as definedin claim 23 further comprising a machining enclosure defined by said onepanel, a plurality of adjoining walls and a moveable access door, saidchuck extending into said machining enclosure so that debris generatedduring the machining operation is confined within said enclosure.